This invention concerns a valve assembly that may be used, for example, to vent fluid from or inject gas into a well annulus.
Annulus valves are used for injecting pressurized gas into well annuli, such as during petroleum production using gas lift. They are also used to bleed fluid from well annuli, to prevent pressure buildups that would otherwise damage the casing program. Conventionally, such annulus valves are situated in a conduit extending through the side wall of a wellhead.
Regulatory authorities generally require that at least two independent pressure barriers be provided in series between the pressurized volume within the well and the well exterior. In the case of annulus valves, an annulus safety valve positioned downhole in the annulus is often used to provide the necessary primary pressure barrier. Replacement or servicing of the annulus safety valve is a lengthy and expensive operation, as it will require removal of the tubing and tubing hanger.
The present invention aims to mitigate the foregoing problem and accordingly provides a well valve assembly comprising a passage extending through a side wall of a wellhead; and first and second valves each positioned to selectively open or close the passage, the second valve in use being located in the passage, towards the well interior with respect to the first valve, and being installable and retrievable through the passage. The second valve can therefore be removed for repair or renewal without disturbing other wellhead components such as the tubing hanger and tubing. Relatively compact, lightweight and unsophisticated pressure containment equipment, such as a lubricator of the kind normally used to install VR (valve removal) plugs in surface wellheads, can be used to maintain pressure integrity of the well and manipulate the second valve into its installed position in the passage.
Preferably, the second valve is installable and retrievable through the first valve, so that no need exists to disturb the first valve and the first valve can therefore remain available to close the passage.
The second valve is preferably remotely, for example hydraulically, actuated. It may be biased towards the closed position, to provide fail safe closure of the passage. The closure bias may be provided by one or more Belleville springs and/or fluid pressure. The Belleville springs may be housed in a chamber isolated from the passage and from the well exterior, to avoid problems of contamination, erosion and corrosion.
The second valve may take the form of a check valve which is closeable by engagement of a closure member with a valve seat to form a metal to metal seal. The closure member is preferably slidable in a tubular valve body which is received in the passage. A hydraulic chamber may be defined between the closure member and the body for actuation of the valve. The closure member may be held in the body by a retainer cartridge, a further hydraulic chamber being defined between the closure member, the body and the cartridge.
The valve seat may be formed annularly about the body interior, and the closure member may be hollow so as to comprise an open end and a blind end, a shoulder being formed about the blind end for co-operation with the valve seat, and radial ports extending from an exterior surface of the closure member behind the shoulder to the hollow interior of the closure member.